all: Remove usage of deprecated io/ioutil (#7971)

As of Go 1.16 io/ioutil is deprecated. This replaces usage with the
corresponding functions in package os and package io.

lib/osutil/atomic.go

@@ -43,7 +43,7 @@ func CreateAtomic(path string) (*AtomicWriter, error) {
 // permissions.
 func CreateAtomicFilesystem(filesystem fs.Filesystem, path string) (*AtomicWriter, error) {
 	// The security of this depends on the tempfile having secure
-	// permissions, 0600, from the beginning. This is what ioutil.TempFile
+	// permissions, 0600, from the beginning. This is what os.CreateTemp
 	// does. We have a test that verifies that that is the case, should this
 	// ever change in the standard library in the future.
 	fd, err := TempFile(filesystem, filepath.Dir(path), TempPrefix)

lib/osutil/atomic_test.go

@@ -8,7 +8,6 @@ package osutil
 
 import (
 	"bytes"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"testing"
@@ -35,7 +34,7 @@ func TestCreateAtomicCreate(t *testing.T) {
 		t.Fatal("written bytes", n, "!= 5")
 	}
 
-	if _, err := ioutil.ReadFile("testdata/file"); err == nil {
+	if _, err := os.ReadFile("testdata/file"); err == nil {
 		t.Fatal("file should not exist")
 	}
 
@@ -43,7 +42,7 @@ func TestCreateAtomicCreate(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	bs, err := ioutil.ReadFile("testdata/file")
+	bs, err := os.ReadFile("testdata/file")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -62,7 +61,7 @@ func TestCreateAtomicReplaceReadOnly(t *testing.T) {
 func testCreateAtomicReplace(t *testing.T, oldPerms os.FileMode) {
 	t.Helper()
 
-	testdir, err := ioutil.TempDir("", "syncthing")
+	testdir, err := os.MkdirTemp("", "syncthing")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -75,7 +74,7 @@ func testCreateAtomicReplace(t *testing.T, oldPerms os.FileMode) {
 		t.Fatal(err)
 	}
 
-	if err := ioutil.WriteFile(testfile, []byte("some old data"), oldPerms); err != nil {
+	if err := os.WriteFile(testfile, []byte("some old data"), oldPerms); err != nil {
 		t.Fatal(err)
 	}
 
@@ -103,7 +102,7 @@ func testCreateAtomicReplace(t *testing.T, oldPerms os.FileMode) {
 		t.Fatal(err)
 	}
 
-	bs, err := ioutil.ReadFile(testfile)
+	bs, err := os.ReadFile(testfile)
 	if err != nil {
 		t.Fatal(err)
 	}

lib/osutil/atomic_unix_test.go

@@ -12,7 +12,6 @@
 package osutil
 
 import (
-	"io/ioutil"
 	"os"
 	"syscall"
 	"testing"
@@ -24,7 +23,7 @@ func TestTempFilePermissions(t *testing.T) {
 	oldMask := syscall.Umask(0)
 	defer syscall.Umask(oldMask)
 
-	fd, err := ioutil.TempFile("", "test")
+	fd, err := os.CreateTemp("", "test")
 	if err != nil {
 		t.Fatal(err)
 	}

lib/osutil/osutil_test.go

@@ -7,7 +7,7 @@
 package osutil_test
 
 import (
-	"io/ioutil"
+	"io"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -83,7 +83,7 @@ func TestIsDeleted(t *testing.T) {
 func TestRenameOrCopy(t *testing.T) {
 	mustTempDir := func() string {
 		t.Helper()
-		tmpDir, err := ioutil.TempDir("", "")
+		tmpDir, err := os.MkdirTemp("", "")
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -131,7 +131,7 @@ func TestRenameOrCopy(t *testing.T) {
 			if err != nil {
 				t.Fatal(err)
 			}
-			buf, err := ioutil.ReadAll(fd)
+			buf, err := io.ReadAll(fd)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -147,7 +147,7 @@ func TestRenameOrCopy(t *testing.T) {
 		if fd, err := test.dst.Open("new"); err != nil {
 			t.Fatal(err)
 		} else {
-			if buf, err := ioutil.ReadAll(fd); err != nil {
+			if buf, err := io.ReadAll(fd); err != nil {
 				t.Fatal(err)
 			} else if string(buf) != content {
 				t.Fatalf("expected %s got %s", content, string(buf))

lib/osutil/traversessymlink_test.go

@@ -7,7 +7,6 @@
 package osutil_test
 
 import (
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -18,7 +17,7 @@ import (
 )
 
 func TestTraversesSymlink(t *testing.T) {
-	tmpDir, err := ioutil.TempDir(".", ".test-TraversesSymlink-")
+	tmpDir, err := os.MkdirTemp(".", ".test-TraversesSymlink-")
 	if err != nil {
 		panic("Failed to create temporary testing dir")
 	}
@@ -71,7 +70,7 @@ func TestTraversesSymlink(t *testing.T) {
 }
 
 func TestIssue4875(t *testing.T) {
-	tmpDir, err := ioutil.TempDir("", ".test-Issue4875-")
+	tmpDir, err := os.MkdirTemp("", ".test-Issue4875-")
 	if err != nil {
 		panic("Failed to create temporary testing dir")
 	}